Electro-thermal actuator



March 4, 1969 R. D. POULIOT 3,430,440

ELECTRO-THERMAL ACTUATOR Original Filed June '7. 1963 Richard 0. Pou/iof INVENTOR ATTORNEY United States Patent 3,430,440 ELECTRO-THERMAL ACTUATOR Richard I). Pouliot, Shrewsbnry, Mass., assignor t0 Reuriden Corporation Continuation of applications Ser. No. 286,297, June 7, 1963, Ser. No. 415,851, Nov. 24, 1964, and Ser. No. 477,520, Aug. 5, 1965. This application Dec. 23, 1966, Ser. No. 621,086 US. C]. 60-23 6 Claims Int. 'Cl. F03g 7/06; F01k 27/00 ABSTRACT OF THE DISCLOSURE This invention relates to an electro-thermal actuator and, more particularly, to an actuator consisting of a housing containing a thermally-expansible material, a piston slidable in and out of the housing, and an electrically-energized heater for raising the temperature of the material to force the piston out of the housing.

This is a continuation of my patent applications Ser. No. 286,297, filed June 7, 1963, now abandoned, Ser. No. 415,851, filed Nov. 24, 1964, now abandoned, and Ser. No. 477,520, filed Aug. 5, 1965, now abandoned.

There are many applications in which it would be useful to have a compact electrical-mechanical transducer, i.e., a motor producing linear action in response to an electrical signal. In the past, motors of this type have been constructed which make use of an electrical resistance which causes mechanical movement by action of heat on a thermally expansible material. However, such prior art motors have suffered from a number of defects. They have been complicated and expensive and, in general, have been unreliable. They have not acted promptly in response to the electrical signal and have presented considerable problem insofar as leakage of operating liquid and the like are concerned. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide an electro-thermal actuator giving linear action in response to an electrical signal.

Another object of this invention is the provision of an actuator consisting of an electrical-mechanical transducer which is simple in construction, inexpensive to manufacture, and which is capable of a long and useful life of maintenance-free service.

A further object of the present invention is the provision of an actuator making use of a thermally-expansible liquid contained in a housing in which provision is made to assure that there is no leakage of the expansible liquid.

It is another object of the instant invention to provide an actuator using a thermally-expansible liquid which is quick to react in response to an electrical signal received from an exterior source, the motor functioning to give a maximum linear motion in a controlled time lapse.

It is a further object of the invention to provide an actuator in which the main operating element may be readily removed for the introduction of operating fluid.

With these and other objects in view, as will :be apparcut to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawing in which:

The single figure is a longitudinal sectional view of an actuator embodying the principles of the present invention.

Referring to the drawing, the actuator, indicated generally by the reference numeral 10, is shown as consisting of a housing 11 carrying a piston 12 and of a body 13 of thermally-expansible material, such as a liquid in which is carried an electrical heating element 14. The housing is of generally tubular form and is provided with a main bore 15. One end of the bore is provided with a groove 16 in which resides a disk-like head 17 and a flange 18 which extends inwardly to lock the head 17 in place. The assembly of the head and the housing 11 takes place in the following manner: as originally constructed, the groove 16 is a counterbore and the flange 18 extends axially of the housing. In assembly, after the head 17 has been slipped in the counterbore the flange 18 is bent radially inwardly by a swaging operation. Extending from the opposite ends of the heating element 14 are leads 19 and 21 adapted to be connected to a source of electrical power (not shown).

The other end of the housing is also provided with a radial groove 22 in which reside the outer peripheries of a head 23, an elastomer body or rubber block 24, and a retainer 25, these elements being locked in the groove by an inwardly-directed flange 26. These elements are locked in place in the same manner that the head 17 is held in its end of the housing; that is to say, the groove 22 is originally a counterbore in which the elements 23, 24, and 25 are placed. Then, the flange 26 (which originally extended axially) is swaged radially inwardly to lock the elements together.

The head 23 consists of a disk-like :body 27 which is locked in the groove 22 and from the center of which emerges an axially-extending neck 28. The neck extends axially outwardly of the body 11 and is provided with a central bore 29. In this bore resides the piston 12, which, for the purposes of illustration, is shown as a rod-like member having an outer head 31 which is substantially larger than the bore 29. The outer end of the rod 32 can be formed with various geometric shapes so that it can be used to function in various applications. This head is adapted to be connected to mechanisms which are to be moved; in other words, the linear motion resulting from the motor action takes place on this head and is transferred to other elements of the mechanism in which the motor is incorporated. The piston 12 is provided with a piston rod 32 which is formed with a recess such as the flat 33 which extends along the length of the piston rod 32 a substantial distance. The recess, however, may take the form of a slot or a relief. Extending transversely across the neck 28 of the head 23 is a bore 34 through which extends a pin 35. The bore 34 has its axis generally tangential to the bore 29 so that a substantial portion of the pin 35 extends upwardly into the flat 33 and, therefore, is capable of limiting the lengthwise movement of the piston 12. The inner end of the piston is shown as an extension of the piston rod 32 and it is provided with no enlarged head.

The inwardly-facing surface of the body 27 of the head 23 is provided with a counterbore 37 which resides a washer-shaped seal member 38. The retainer 25 is made out of sheet metal and is in the shape of a hat having a flange which is held in the groove 22 and a crown which extends axially into the chamber of the housing. The retainer is provided with a circular aperture 39 through which the piston 12 passes and which is larger than the piston. The elastomer body 24 is interposed and prestressed between the transverse surface of the body 27 of the head 23 and the outwardly-directed surface of the retainer 25. It is, therefore, of a generally hat-shaped conformation and is provided with a central axis bore 41 which is of approximately .020 less in diameter than the diameter of the piston so that it embraces the piston 12 the end of the housing produces an additional prestress in the rubber block 24, thus producing even further pres sure of the rubber on the piston. The thermally-expansive material may be any one of a number of suitable chemicals, such as the fiuoro-chemicals. In general, they should be selected to have a high coefiicient of thermal expansion, a high thermal conductivity, they should be nonelectrically conductive (good insulators), they should be of such a nature as to be noncorrosive so far as the housing and the elastomer body are concerned, and, of course, they should be fairly inexpensive. The elastomer body 24 may be formed of rubber, or a rubber-like artificial material, such as Teflon or butadiene.

The operation of the invention will now be readily understood in view of the above description. The actuator will normally appear in the condition shown in the drawing. In this condition, the elastomer body 24 is in a prestressed condition and the retainer 25 is in its expanded position. The piston 12 is in its left-hand position in the drawing with the retaining pin 35 residing at the righthand end of the flat 33 on the side of the piston. Presumably, also, the head 31 can be pressed against the outboard end of the neck 28 of the head 23 or head 31 can be located by pin 35 in the flat 33. The body 13 of thermally-expansible liquid is cold and is in a shrunken condition. When it is desired to energize the motor to operate a mechanism, an electrical current is connected across the leads 19 and 21 so that an electrical current flows through the heating element 14, the heating element being embedded in the body 13 of thermally-expansible liquid. The material immediately begins to heat and to react to the heat and it begins to increase in volume. When it does so increase, it presses in all directions against all parts of the inside of the housing 11 and all articles contained therein, one of the set of surfaces being the surface of the piston 12. Particularly, the shaped surface 36 thereof receives the full stress of the added pressure. The piston, therefore, moves outwardly of the housing 11, through the bore 41 in the elastomer body 24, through the aperture 39 in the retainer 25 and through the bore 29 in the head 23. As the body 13 expands the piston is forced outwardly more and more until, eventually, it reaches the position in which the pin 35 resides at the left-hand side of the flat 33 in the piston, thus limiting the motion. Whatever mechanism is attached to the head 31 has been actuated through a full stroke of the motor. The expanding of the liquid body 13, of course, Operates on the surface of the body 24 through the aperture 39 which serves it to compress the elastomer body 24 and to cause it to press tightly around the surface of the piston 12 as it slides through the bore 41. The removal of the electrical current from the leads 19 and 21, thus causing a drop or substantial decrease or termination of passage of current through the heating element '14, causes the body 13 to cool down so that the piston 12 is free to reenter the housing 11 and to reside with its head 31 residing against the outer end of the neck 28. The elastomer body 24 acts as an alignment guide and seal for the piston 32 during linear motion.

It can be seen that, since'the heating element is embedded deeply in the body 13, any heating of the heating element due to electrical current passing through it is quick to react on the thermally-expansive material so that the actuator operates very readily. Also, it is a simple matter to dismantle the piston and replace it by removing the pin 35, so that the piston is free to leave the housing. The operation of the pressure of the thermally-expansive material 13 on the body 24, thus compressing it, causes a very tight seal so that there is no danger of leakage of the material around the exit of the piston. The greater the pressure of the liquid, the greater the sealing effect.

It is obvious that minor changes may be made in the form and construction of the invention Without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such forms as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

1. An actuator, comprising:

(a) a housing including an end wall,

(b) a nonelectrically conductive, thermally-expansible material in the housing,

(c) a piston rod movable in the housing and movable through an aperture in the said end wall in response to expansion of the material,

(d) an electrical heating element in the material and having leads extending exteriorly of the housing,

(e) a block of elastomer material encasing the piston rod on its perimeter and extending between the piston rod and the housing, the block engaging the said end wall and the piston rod extending entirely through the block and the wall the configuration of the block being such that the surface area facing away from the said end wall is substantially greater than the surface area facing toward the end wall, and

(f) a rigid restraining member encasing the block to press it against the piston rod at all times, an aperture extending through the restraining member to permit at least a portion of the block to be acted upon by the said material whereby, as the pressure in the material increases, the pressure of the block on the piston rod also increases.

2. An actuator, as recited in claim 1, wherein the housing is provided with an axially-elongated cylinder in which the piston rod resides.

3. An actuator, as recited in claim 1, wherein the thermally-expansible liquid occupies the entire volume of the housing exclusive of the piston rod, the heating element, and the block.

4. An actuator, comprising:

(a) a housing,

(b) a nonelectrically conductive, thermally-expansible liquid in the housing,

(c) a piston rod movable in the housing and movable in response to expansion of the liquid,

(d) a separate electrical heating element in the liquid and having leads extending exteriorly of the housing,

(e) a block of prestressed elastomer material surrounding the piston rod and extending between the piston rod and the housing, the block engaging an end wall of the said housing and the piston rod extending entirely through the block and the wall, and

(f) a rigid restraining member encasing the block to press it against the piston rod at all times, the member and the block being acted upon by the said liqiud whereby, as the pressure in the liquid increases, the pressure of the block on the piston rod and on the said end wall increases to provide greater sealing against escape of the liquid from the housing.

5. An actuator as recited in claim 4, wherein the outer portion of the block is locked to the housing to obviate a gap therebetween.

6. An actuator as recited in claim 5, wherein the elastomer material in the block and the locking of the block to the housing is brought about by crimping the housing around the end wall.

References Cited UNITED STATES PATENTS 961,865 6/1910 Kleinhan. 1,822,408 9/ 193 1 King. 2,208,149 7/ 1940 Vernet. 2,806,375 9/1957 Wood. 2,835,634 5/1958 Vernet et al 60-23 X 2,928,233 3/ 1960 Kimm 60-23 2,960,303 11/1960 Smallpeice 60-23 X 3,075,348 1/ 1963 Baker 60--23 EDGAR W. GEOGHEGAN, Primary Examiner. 

